1. Field of the Invention
The present relates to a laying device for laying a line element connected to a tool attached to a forward end of an arm of a robot. The laying device according to the present invention is typically used for laying line elements such as electric and/or fluid supply lines in a forward end of an arm of an industrial robot.
2. Description of the Related Art
Most of tools attached to a forward end of an arm of a robot need a supply of electric signals, electric power, or a fluid such as a gas or a liquid, as is well-known. Also, signal lines are often necessary for transferring signals from a tool side to a robot controller or the like. Therefore, a way of laying line elements, connected to the tool attached to the forward end of the robot arm, is important.
Conventional ways of laying line elements extending up to the forward end of the wrist portion of the robot arm are as follows.
(1) A way of arranging the line elements such that they extend on the exterior of the robot arm and are directly connected to the tool:                When this way is used, some means are necessary for preventing the line elements from abrading against or being entangled around the arm or the wrist portion. One of them is to provide a bracket for hanging a bundle of the line elements via a spring and to connect the line elements via the bracket to the tool at the forward end of the wrist portion. Japanese Unexamined Patent Publication No. 2001-150382 also suggests a way of using a line element guide bracket for absorbing a motion of the wrist portion in order to reduce the degree of abrasion or entanglement.        
(2) A way of relaying the line elements in a radial direction of the wrist portion near a tool mount surface (flange) of the wrist portion:                This way is described in Japanese Unexamined Patent Publication No. 10-329079. A hollow portion extending along a rotation axis of the wrist portion of the robot is formed in a center portion of the forward end of the wrist portion of the robot, so that the line elements can pass through the hollow portion. The line elements extending through the hollow portion are directed in a radial direction of the wrist portion near the tool mount surface and then relayed by couplings or connectors extending in the radial direction of the wrist portion to be connected to the tool. This way makes it possible to lead the line elements to the tool without exposing the line elements to the exterior.        
(3) A way of directing the line elements in the direction of a rotation axis of the wrist portion near a tool mount surface of the wrist portion and relaying them in the direction of the rotation axis:                This way can be also one of several usable ways. However, as longitudinally extending portions of connectors or the like are liable to interfere with the tool, the application of this way is often limited to the case in which elbow-type connectors or couplings are employed. As a special example, Japanese Unexamined Patent Publication No. 2002-79487 suggests a way of combining a tool mount surface and an automated tool changing apparatus to simplify the handling of the line elements. In this way, a hollow portion extending along the rotation axis of the wrist portion of the robot is formed in a center portion of the forward end of the wrist portion, so that the line elements can pass through the hollow portion. Further, the ends of the line elements are arranged circumferentially on the tool mount surface, so that a connection and disconnection of all line elements is performed at once in the direction of the rotation axis when a tool is changed.        
(4) Other ways of relaying the line elements:                In other ways of relaying the line elements in the wrist portion of the robot, a rotary joint for connecting the line elements between portions rotated relative to each other (as described in Japanese Unexamined Patent Publication Nos. 5-138580 and 5-293788) or an automated tool changing apparatus for performing a connection and disconnection of the line elements at once in order to allow various kinds of tools to be changed and used at the forward end of the wrist portion (as described in Japanese Unexamined Patent Publication No. 11-504869), etc. can be used.        
However, the above-mentioned prior arts have various following problems.
In the first way (1) of arranging the line elements such that they extend on the exterior of the robot arm and are directly connected to the tool, the line elements are exposed as a whole, and therefore, are liable to be damaged by coming into contact with, or getting entangled around, the arm portion or the wrist portion of the robot and peripheral devices. Further, in order to replace the line elements, all of a long section from the tool to a root of the arm must be replaced. Therefore, the replacement of the line elements requires a long time and is expensive, and the maintenance is not easy.
In the above-mentioned way (2) of relaying the line elements in the radial direction of the wrist portion near the tool mount surface of the wrist portion, the line elements are relayed at the wrist portion. Therefore, for example, if a portion of a cable extending ahead of the wrist portion is damaged, only a short section of the line element has to be replaced. As the portion of the cable extending ahead of the wrist portion is generally liable to be damaged, this way has an advantage in maintenance. On the other hand, this way has a disadvantage in which the connectors or couplings used in the relaying portion extend in the radial direction of the wrist portion and therefore a maximum external diameter of the relaying portion including the connectors, etc., must be large.
In other words, an interference area of the relaying portion in operation is very large, which increases possibility of the relaying portion coming into contact with external devices. Further, the larger interference area makes the relaying portion more liable to come into contact even with the other portion of the robot. Therefore, in some cases, an operation range may be restricted. Further, the cables or hoses are required to be movable within the hollow portion, and a mechanism for sealing the hollow portion is necessary to prevent dusts or the like from entering the hollow portion.
When the above-mentioned way (3) of relaying the line elements in the direction of the rotation axis of the wrist portion near the tool mount surface of the wrist portion is employed, the interference between the connectors or couplings and the tool is liable to occur. Thus, in order to avoid this interference, it is required to use elbow type connectors or couplings, thereby preventing the protrusion of the connectors or couplings from the tool mount surface and to make a member (rotation shaft member) formed with the tool mount surface have a larger dimension in a longitudinal direction of the arm. This causes problems of resulting in an increased distance from the arm to the tool and an increased load on the wrist portion.
The above-mentioned way (4) also has a disadvantage. For example, in the way of using the rotary joint as described in Japanese Unexamined Patent Publication No. 5-293788 and the way of combining the relaying portion and the automated tool changing apparatus as described in Japanese Unexamined Patent Publication No. 11-504869, the connection of the connectors is performed in the radial direction. Therefore, the relaying portion has a large maximum external diameter and a complex structure, and is expensive.